Current power sensing devices often take the form of a shunt diode, which is tapped off of an interstage matching network of a power amplifier. An example of a device of this type is provided in FIG. 1. Such a diode rectifies a voltage wave, which is proportional to the output power of the total amplifier. This yields a DC voltage that is a non-linear function of the transmitted output power from the power amplifier. A relationship between the DC voltage output from the diode rectifier, and the output power of the power amplifier may be established using well-known methods. It is also known in the art that the detection of output power of a power amplifier may be accomplished by the use of a forward directional coupler, which is coupled to a diode detector at the output of the amplifier. The diode detector operates to detect and rectify a power wave proportional to the output power of the power amplifier. Such a device is illustrated in FIGS. 2 and 3A-B. A number of problems, however, exist with each of the above devices.
First, the use of an internal diode detector requires that it be by-passed using a large value capacitor, as well as low pass filter, for holding the diode rectified voltage which is a function of the incident power onto the diode detector. Such a circuit requires a relatively large area semiconductor (for example, a large area of gallium arsenide) in order to properly implement such a circuit. Furthermore, the use of an output forward directional coupler to sample and rectify the output power of the power amplifier results in an additional expense associated with the circuit. Moreover, the use of an ouput forward directional coupler also requires a temperature compensated diode detector circuit, resulting in additional cost and complexity to the sensing circuit.
Accordingly, a device which replaces each of the above components and which utilizes a single semiconductor structure that is both small and compact is highly desirable.